Skimmer, barge and methods for recovering and transferring heavy oil or bitumen

ABSTRACT

Skimmers, barges and related methods recover heavy oil or bitumen from contaminated water environments such as tailings ponds. The skimmer has an articulated mesh-like conveyor driven around a drum by a drive sprocket. A pusher mechanism discharges bitumen or heavy oil from cavities in the conveyor. In one embodiment, the skimmer includes an automatic depth control system. In other embodiments, knife-edged shear plates remove heavy oil or bitumen adhering to the conveyor and drum. A barge may incorporate multiple parallel skimmers. The barge may include a bitumen-transfer pump having an annular fluid-injection flange that generates an annulus of lubricating fluid inside a discharge hose. A method of skimming heavy oil or bitumen involves using a skimmer that automatically adjusts its elevation or depth based on a control signal generated by a depth sensor. Another method recovers and transfers bitumen by lubricating the discharge hose using the annular fluid-injection flange.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims the benefit of priority from CanadianPatent Application No. 2,731,868, filed Feb. 16, 2011, the contents ofwhich are herein incorporated by reference in their entirety.

TECHNICAL FIELD

The present invention relates generally to skimmers for removing oilcontaminants from a water environment and, in particular, to skimmingheavy oil or bitumen from a water environment such as a tailings ponds.

BACKGROUND

Bituminous sands (also known as oil sands or tar sands are sands thatcontain sand, clay, water, and a dense and very viscous petroleum knownas bitumen. Oil sands are developed through two methods: open-pit miningand deep underground production. In open-pit mining, hot water isemployed for separating bitumen from the sand. This water is then sentto a tailings pond. The tailings ponds are an environmental concern. Forexample, these ponds have been harmful to migrating birds. Efforts arecontinually being made to recover the heavy oil and bitumen from thesetailings ponds and to clean and rehabilitate contaminated bodies ofwater.

Applicant developed and patented some early skimmer technologies thatused a continuous conveyor to skim heavy oil or bitumen.

The first is disclosed in U.S. Pat. No. 5,743,694 (Hines) entitled “OilRecovery Apparatus”. This patent disclosed an open-mesh conveyordesigned to slope from a vessel into the contaminated water and to runwith the lower flight of the conveyor travelling inboard over a flatbottomed trough.

An improvement on the technology disclosed in U.S. Pat. No. 5,743,694 isdisclosed in U.S. Pat. No. 6,328,888 (Hines) entitled “Skimmer”. Thelatter patent disclosed a conveyor which utilizes a press roller orother mechanical pusher elements to push the extremely viscous heavy oilor bitumen from the cavities defined by the mesh of the conveyor into aholding tank.

Despite this improvement, very substantial technical challenges remain.Recovering the extremely viscous and sticky bitumen or heavy oil from acontaminated water environment such as a tailings pond is verychallenging for a number of reasons. For example, the bitumen or heavyoil adheres to the skimmer mechanism, interfering with the smoothoperation of the conveyor and inhibiting discharge from the conveyor.Effective skimming is also highly sensitive to the precise placement andorientation of the skimmer relative to the heavy oil or bitumen floatingon the surface of the contaminated water environment. Another problemarises when attempting to transfer bitumen to shore from the holdingtank on the barge. Therefore, there exists a need in the oil industryfor a more effective skimmer and barge and for more effective methods ofskimming bitumen and heavy oil.

SUMMARY

The present invention, in general, provides novel skimmers for skimmingheavy oil or bitumen as well as novel barges for recovering andtransferring heavy oil or bitumen from the barge to shore or to anothervessel. The present invention also provides related methods forrecovering and transferring heavy oil or bitumen from a contaminatedwater environment.

In accordance with one main aspect of the present invention, a skimmerincludes a frame for supporting a drive sprocket and for supporting adrum. The skimmer includes a conveyor driven around the drum by thedrive sprocket, the conveyor defining a downwardly moving upper flightand an upwardly moving lower flight. A skimmer also includes a troughdisposed below a portion of the lower flight, the trough extending fromthe drum to a discharge opening. The skimmer further includes a pushermechanism disposed at the discharge opening to force bitumen or heavyoil from the conveyor into the discharge opening. The skimmer furtherincludes a shear plate disposed at the discharge opening, wherein theshear plate has a knife-edge for cutting away bitumen or heavy oiladhering to the conveyor.

In accordance with another main aspect of the present invention, askimmer includes a frame for supporting a drive sprocket and forsupporting a drum. The skimmer includes a conveyor driven around thedrum by the drive sprocket, the conveyor defining a downwardly movingupper flight and an upwardly moving lower flight. The skimmer alsoincludes a trough disposed below a portion of the lower flight, thetrough extending from the drum to a discharge opening. The skimmerfurther includes a pusher mechanism disposed at the discharge opening toforce bitumen or heavy oil from the conveyor into the discharge opening.The skimmer further includes a shear plate disposed at the drum, whereinthe shear plate has a knife-edge for cutting away bitumen or heavy oiladhering to the drum.

In accordance with another main aspect of the present invention, askimmer includes a frame for supporting a drive sprocket and forsupporting a drum. The skimmer includes a conveyor driven around thedrum by the drive sprocket, the conveyor defining a downwardly movingupper flight and an upwardly moving lower flight. The skimmer alsoincludes a trough disposed below a portion of the lower flight, thetrough extending from the drum to a discharge opening. The skimmerfurther includes a pusher mechanism disposed at the discharge opening toforce bitumen or heavy oil from the conveyor into the discharge opening.The skimmer further includes a shear plate disposed at the drum, whereinthe shear plate has a knife-edge for cutting away bitumen or heavy oiladhering to the drum.

In accordance with yet another main aspect of the present invention, abarge for recovering heavy oil or bitumen includes a floating structureadapted to float on a surface of a contaminated water environment and aplurality of parallel skimmers mounted to the floating structure.

In accordance with yet another main aspect of the present invention, abarge for the recovery and transfer of bitumen includes a floatingstructure adapted to float on a surface of a contaminated waterenvironment, at least one skimmer mounted to the floating structure forrecovering bitumen from the surface of the contaminated waterenvironment and for discharging the bitumen into a holding tank, and abitumen-transfer pump disposed in the holding tank for transferring thebitumen through a discharge hose, wherein the bitumen-transfer pumpincludes an annular fluid-injection flange for generating an annularbarrier of fluid inside the discharge hose to lubricate the inside ofthe discharge hose.

In accordance with yet a further main aspect of the present invention, amethod of skimming heavy oil or bitumen entails disposing a skimmerhaving a conveyor in a water environment contaminated with heavy oil orbitumen, operating the conveyor of the skimmer to recover the heavy oilor bitumen from the water environment, and automatically controlling adepth of the skimmer using an automatic depth control system thatreceives a control signal from a depth sensor connected to the skimmer.

In accordance with yet a further main aspect of the present invention, amethod of recovering bitumen from a contaminated water environment. Themethod entails skimming the bitumen from a surface of the contaminatedwater environment, wherein skimming includes discharging skimmed bitumeninto a holding tank, and pumping the bitumen from the holding tank usinga transfer pump connected to a discharge hose. The transfer pump mayinclude an annular fluid-injection flange for generating a lubricatingannulus of fluid to facilitate transfer of the bitumen through thedischarge hose.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features and advantages of the present technology will becomeapparent from the following detailed description, taken in combinationwith the appended drawings, in which:

FIG. 1 is a perspective view of a barge and skimmer in accordance withan embodiment of the present invention;

FIG. 2 is a top view of the mesh-like structure of the conveyor used inthe skimmer of FIG. 1;

FIG. 3 is a side elevation view of a skimmer in accordance with anembodiment of the present invention;

FIG. 4 is a view of the lower flight of the conveyor of the skimmer ofFIG. 3;

FIG. 5 is a side elevation view of a barge in accordance with anembodiment of the present invention; and

FIG. 6 is a plan of the main deck of the barge of FIG. 5;

FIG. 7 is a plan of the hold of the barge of FIG. 5;

FIG. 8 is a front view of an annular fluid-injection flange for thetransfer of bitumen; and

FIG. 9 is a cross-sectional view of the flange of FIG. 8.

DETAILED DESCRIPTION

In general, and by way of overview, the present invention provides novelskimmers, heavy oil and bitumen recovery and transfer barges and relatedmethods of skimming and transferring heavy oil and bitumen.

The entire disclosures of U.S. Pat. No. 5,743,694 (Hines) entitled “OilRecovery Apparatus” and U.S. Pat. No. 6,328,888 (Hines) entitled“Skimmer” are hereby incorporated by reference.

Skimmer

In the embodiments depicted by way of example in the appended figures,the skimmer 100 has a conveyor (or conveyor belt) 110 which is used toskim heavy oil or bitumen and to convey the heavy oil or bitumen into aholding tank. This conveyor may be made of metal such as, for example,stainless steel, although other suitable materials may be utilized. Thisconveyor may, for example, be mounted to a barge 300 as shown in FIG. 1.

As depicted by way of example in the figures, the conveyor may be anarticulated open mesh (as depicted particularly in FIG. 2) defining aplurality of cavities 120 for collecting and transporting the heavy oilor bitumen. An example of a suitable mesh structure for the conveyor isdisclosed in U.S. Pat. No. 6,328,888.

In the depicted embodiments, the conveyor may be efficiently driven by adrive sprocket 130 having teeth 132 or cogs that mesh with the cavitiesof the mesh-like structure of the conveyor. As shown by way of example,the conveyor travels around a drum 140 or roller which is a passivecylindrical or tubular component. The drum may be replaced by anysuitable idler, wheel or any suitable combination of passive rollingelements.

In the embodiments illustrated, the skimmer 100 has a frame 102 thatsupports a conveyor 110 that travels in a clockwise direction whenviewed from its left side (i.e. when viewed in the manner depicted inFIG. 3). The direction of travel of the conveyor means that an upperflight 112 of the conveyor travels in a downwardly sloping manner fromthe drive sprocket to the drum whereas a lower flight 114 of theconveyor travels in an upwardly sloping manner from the drum to thedrive sprocket. Heavy oil or bitumen is thus collected by the cavitiesof the mesh-like conveyor as the conveyor dips into the bitumen or heavyoil floating on the surface of the tailings pond or other body of water.The collected bitumen or heavy oil is then conveyed upwardly toward adischarge opening 116 where it discharges into a containment tank orholding tank in the barge.

Because of the extremely high viscosity of the bitumen or heavy oilbeing conveyed, the bitumen or heavy oil will resist falling naturally(under the effect of gravity) into the containment tank. Therefore, tofacilitate the discharge from the conveyor, a pusher mechanism 118 isprovided. The pusher mechanism may be a press roller of the typedisclosed in U.S. Pat. No. 6,328,888. This press roller has teeth thatare adapted by their shape and size to press the heavy oil or bitumenfrom the cavities. Other non-rotary presses or pushing elements may beutilized.

A trough or tray 122 extends as shown by way of example in the figuresfrom the bottom of the lower flight to a discharge opening where thebitumen or heavy oil discharges into the containment tank. The trough(tray) protects the barge from any bitumen or heavy oil that detachesprematurely from the conveyor while it is being conveyed up to thedischarge opening.

Because the bitumen or heavy oil tends to adhere or cling to theconveyor, a shear plate 150 is provided to cut away the bitumen or heavyoil from the conveyor so that the bitumen or heavy oil falls into thecontainment tank disposed below the discharge opening. This top shearplate may be disposed at a top of the lower flight of the conveyor,adjacent the discharge opening and press roller.

In another main set of embodiments, this top shear plate is aknife-edged (or razor-edged) shear plate designed to cut off bitumen.This knife-edged shear plate is an improvement on the flat-faced shearplate of U.S. Pat. No. 6,328,888 because the knife edge cuts the bitumenoff rather than attempting to scrape it off.

The knife-edged shear plate has a razor-sharp blade that may be, forexample, bevelled or cut at 45 degrees to present a sharp but robustleading edge. As shown in the embodiments depicted in the figures, theshear plate points downwardly toward the upper end of the trough tothereby define the discharge opening. In other words, the dischargeopening is defined by the space between the lower edge of theknife-edged shear plate and the upper edge of the trough.

Not only does the bitumen or heavy oil tend to adhere to the conveyor,but it also may adhere to the drum. Accordingly, to address this furtherproblem, in one main set of embodiments, the novel skimmer has a lowershear plate 152 disposed at a bottom of the lower flight of theconveyor. This lower shear plate may have a knife edge (or razor edge)which may or may not be the same as the knife-edged upper shear plate.The lower shear plate cuts off the bitumen to thereby clean the lowerdrum so that the lower drum does not reload the belt with bitumen beforeit has the opportunity to pick up new bitumen from the water surface. Inthe embodiments illustrated, this lower drum-cleaning shear plate pointsdownwardly and is positioned tangentially to the bottom of drum. Bitumenadhering to the drum is sliced off by the lower shear plate and fallsnaturally into the cavities of the conveyor beneath.

Applicant has also recognized that maintaining the skimmer at the rightelevation or depth optimizes its effectiveness. Accordingly, in anothermain set of embodiments, the skimmer has an automatic elevation controlsystem for automatic adjustment of the elevation (or “depth”) of theskimmer. A sensor provides a control signal to a controller which, inturn, controls the hydraulics automatically to regulate the elevation(depth) of the skimmer.

In one implementation, the sensor may be a float bulb which sends anelevation/depth signal to a controller for controlling theelevation/depth of the skimmer. The controller may be anymicroprocessor, processing unit, computer, etc. In one implementation,the controller automatically controls a pair of hydraulic cylinders 180to raise and lower the skimmer. In another implementation, onecontroller receives control signals from multiple sensors andindividually controls multiple parallel skimmers based on theirrespective control signals.

While the three new features described above (top knife-edged shearplate, bottom drum-cleaning shear plate, and automatic elevationcontrol) may be used independently of one another in different variantsof the skimmer, for optimal performance, the skimmer should employ allthree of these features, i.e. the skimmer should include the knife-edgedtop shear plate, the knife-edged bottom shear plate, and the automaticelevation control system. Using all three of these novel featuresenables the skimmer to operate with utmost efficiency and effectiveness.The elevation/depth control system automatically adjusts the skimmer'sdepth for optimal pick-up of new bitumen or heavy oil while the shearplates cut away bitumen from the conveyor and drum to keep the conveyorrunning efficiently.

Further design features of the skimmer will now be described.

The skimmer may also include four wheel assemblies 160 for displacingthe frame of the skimmer over guide rails 170, as shown by way ofexample in FIG. 1. The wheel assemblies and guide rails together form acarriage assembly for smooth motion of the skimmer when raising orlowering the skimmer into the water. One or more stops on each guiderail 170 is provided to ensure that the skimmer cannot roll into thewater in the unlikely event that the hydraulic cylinders 180 were tofail mechanically. The rails may be affixed (e.g. welded) to the side ofthe barge hull.

In one embodiment, the skimmer includes a trough-tensioning mechanism(or “tray-tensioning mechanism”) for holding the trough (“tray”) at apredetermined distance beneath the lower flight of the conveyor. Thetrough-tensioning mechanism may include a plurality of spring assemblies190 in which coil springs are arranged substantially perpendicular tothe upper and lower flights of the conveyor. Because of the mechanicalelasticity introduced by the spring assemblies 190, the trough 122 candisplace over a limited range to provide a gap sufficient for debris orforeign objects (e.g. branches, stones, animal bones, etc.) having asize up to about 1 inch (2.5 cm) to pass between the lower flight of theconveyor and the trough. Without this spring-loaded trough, debris orforeign objects might cause the conveyor to jam.

The frame of the skimmer may also include four bearing-adjustmentmechanisms 200 for adjusting the relative positions of the left andright bearings 134 of the drive sprocket 130 and the left and rightbearings 144 of the drum 140. These four bearing-adjustment mechanisms200 enable adjustment of the tension in the conveyor 110 by regulatingthe distance between the axes of the drive sprocket 130 and drum 140.The bearing-adjustment mechanisms 200 also permit adjustment of thetracking of the conveyor 110 (to ensure that it tracks correctly foroptimal performance).

The skimmer 100 may also include a funnel and splash guard 210 thatguides material into the holding tank and prevents spattering of oil. Asshown by way of example in FIG. 3 and FIG. 4, this funnel and splashguard 210 may be disposed at the top of the conveyor 110, i.e. at leastpartially enshrouding the drive sprocket.

Barge

The skimmer disclosed above may be mounted to, installed on, orotherwise incorporated into a barge 300. The term “barge” is meant toencompass any type of vessel that is adapted to be used on a tailingspond or contaminated water environment upon whose surface is floating ahighly viscous heavy oil, bitumen or similar substance.

An example of such a barge is shown in the figures although it should beappreciated that the novel skimmer may be mounted to other types ofvessels. As shown by way of example in FIG. 5 to FIG. 7, the barge 300has a hull 302, a main deck 304, railings 306, a pilot house 308, anengine room with engine 310, fuel tanks 312, outboard propulsion system314, a hydraulic power pack 316, a reclaiming tank 318 (also referred toherein as a containment tank, container or holding tank), a crane 320for manipulating the skimmers and transfer pump, a pair of skimmers 100disposed in this exemplary configuration at the front of the barge 300,and a control console 322 for controlling the skimmers. The hull, pilothouse and decks of the barge may be constructed from bare (unpainted)marine grade aluminum (e.g. 5000 or 6000 series) for optimal performancein contaminated water environments, although persons of ordinary skillin the art will appreciate that other materials may be substituted orutilized.

In the embodiment depicted in the figures, the barge has twoside-by-side skimmers. These skimmers may be controlled by a commoncontroller or by two separate controllers. Each of the skimmers may bepowered by a respective pair of hydraulic actuators. Although in theillustrated embodiments the barge has two skimmers, it will beappreciated that the barge may include more than two skimmers. In otherwords, the barge may have any number of parallel replaceable skimmers.

Applicant has discovered that merely widening the skimmer's contactsurface counter-intuitively does not increase performance but actuallydegrades performance due to power requirements and conveyor distortionissues. Accordingly, the barge uses multiple parallel skimmers ratherthan a single wide skimmer. The skimmers may be replaceable modularunits that can be removed for maintenance, overhaul, repair or servicingor replaced by an altogether new skimmer.

In another main set of embodiments, the barge may include a bitumentransfer pump (not illustrated) for transferring bitumen from the bargeto shore (or to another barge or vessel). This bitumen transfer pump maybe disposed in the holding tank. The bitumen transfer pump, in oneembodiment, has an Archimedean screw for displacing the bitumen and anannular fluid-injection flange 400, such as the one shown by way ofexample in FIG. 8 and FIG. 9. As shown in the figures, water or otherlubricating fluid enters the annular fluid-injection flange 400 via aplurality of equidistantly-spaced inlets 402. The annularfluid-injection flange may be constructed of an inner ring 406 and anouter ring 408, as shown by way of example in FIG. 9. The water isredirected through an annular outlet 404 to form an annulus of water.The annular fluid-injection flange 400 thus enables an annulus of fluid,e.g. water, to be injected into the transfer line. The water (or otherfluid) provides an annular water barrier around the discharging,extremely viscous bitumen. Previously, conventional techniques requiredthat bitumen be mixed with a solvent such as naptha. Once thebitumen-naptha mixture reaches its downstream destination, the naptha isthen removed from the bitumen, and recycled back upstream for reuse withthe next amount of bitumen.

An example of a suitable bitumen transfer pump is the FOILEX TDS (“TwinDisc Screw”) pump available from FOILEX Engineering AB (Göteborg,SWEDEN). The FOILEX TDS pumps are designed for off-loading or transferpumping of highly viscous substances such as crude oil, bunker oil andemulsions. These pumps have been found by Applicant to workexceptionally well with bitumen as well provided the annularfluid-injection flange 400 is used to lubricate the discharge hose. Itwill be appreciated that other pumps may be substituted.

In the embodiment illustrated by way of example, the crane 320 may be aknuckle crane or equivalent. This crane is designed for moving thedetachable (replaceable) skimmers and for moving the transfer pump intoand out of the holding tank.

In the embodiment illustrated by way of example, the holding tank 318(i.e. container, containment tank, reclaiming tank) may be, for example,approximately five cubic meters for holding skimmed bitumen or heavyoil, although it will be appreciated that the volume may be varieddepending on the size of the barge or other factors. The transfer pumpis placed in the bottom of the holding tank to transfer skimmed bitumenor heavy oil to shore or to another vessel via a discharge hose or othertransfer means.

In one embodiment, the barge has an oil reservoir that is disposed at abottom inside surface of the hull. This placement of the oil reservoirfacilitates heat transfer to the hull and surrounding body of water,thereby cooling the hydraulic oil.

In one embodiment, the barge has one or more hydraulic outboard drivesfor propulsion. Each propeller 324 is tilt-adjustable andheight-adjustable. The height-adjustable mechanism may optionally belimited so that the propeller can only be lowered as deep as the hullbut no further to ensure that the propeller remains protected by thehull even at its lowest (deepest) position.

Optionally, the barge may include a hitch for towing an object, forexample, for towing a boom, another barge, a smaller watercraft, apontoon skimmer, etc.

Instead of mounting one or more skimmers to a barge, a single skimmermay be pontoon-mounted and controlled remotely by a cable or wirelesslink. The pontoon-mounted single skimmer may be operated by a user onshore or on a nearby barge or vessel. Optionally, two pontoon-mountedsingle skimmers may be attached to the starboard and port sides of thebarge to increase the skimming capacity, e.g. to a total of fourskimmers. These may be connected to the barge using a vertical keywaythat allows vertical self-adjustment of the pontoon-mounted skimmers sothat each one can operate at the optimal depth.

The skimmers may also be adapted for land-based operation. Due to thevariability of the depth from the mounting point on shore, a series ofskimmers may be installed to reach a desired elevation without theassistance of a pump.

Methods

The foregoing skimmer and barge technologies enable various new methodsfor skimming heavy oil or bitumen.

One method is a method of skimming heavy oil or bitumen usingautomatically controlled skimmers. In other words, this method entailsautomatically controlling the elevation (depth) of the skimmer using anelevation sensor (depth sensor) that sends a control signal to acontroller that, in turn, controls the elevation (depth) of the skimmer.This method involves disposing the skimmer in the water. This may beaccomplished by manually operating the hydraulic actuators to lower theskimmer into the water. Once the skimmer is in the water, the automaticelevation control system is activated. This automatic elevation controlsystem continually adjusts the depth of the skimmer to provide optimalskimming performance.

Another method entails recovering bitumen from a bitumen tailings pondor any other contaminated water environment. The method involvesskimming bitumen from the water (e.g. tailings pond), dumping thebitumen into a holding tank and then pumping the bitumen from theholding tank. In one embodiment, the pumping is accomplished using anannular fluid-injection flange which introduces an annulus of fluid suchas water inside the discharge hose around the bitumen being pumped out(to lubricate the discharge hose).

These methods may be performed independently of one another or together.The method of transferring bitumen may be performed without heating thebitumen or, as noted above, mixing the bitumen with any solvent. Thesemethods may be used to recover heavy oil and bitumen from tailings pondsor other bodies of water at any temperature above freezing.

The foregoing technologies are directed to recovery of bitumen or heavyoil. However, the technologies may also be used to recover some mediumoils as well. For the purpose of this specification, it should beunderstood that the term “heavy oil” is meant to encompass petroleum orhydrocarbon substances having a downhole viscosity of 10 to 10,000 cPo(centipoises) whereas the term “bitumen” is meant to encompass oil sandor tar sand substances having a downhole viscosity of greater thanapproximately 10,000 cPo.

The embodiments of the invention described above are intended to beexemplary only. As will be appreciated by those of ordinary skill in theart, to whom this specification is addressed, many obvious variationscan be made to the embodiments present herein without departing from thespirit and scope of the invention. The scope of the exclusive rightsought by the applicant is therefore intended to be limited solely bythe appended claims.

The invention claimed is:
 1. A skimmer comprising: a frame forsupporting a drive sprocket and for supporting a drum; a conveyor drivenaround the drum by the drive sprocket, the conveyor defining adownwardly moving upper flight and an upwardly moving lower flight; atrough disposed below a portion of the lower flight, the troughextending from the drum to a discharge opening; a pusher mechanismdisposed at the discharge opening to force bitumen or heavy oil from theconveyor into the discharge opening; a shear plate disposed at thedischarge opening, wherein the shear plate has a knife-edge for cuttingaway bitumen or heavy oil adhering to the conveyor; and an automaticelevation control system for generating a control signal when sensing anelevation of the conveyor and for automatically controlling theelevation of the skimmer based on the control signal by controllinghydraulic cylinders to cause wheels of the skimmer to roll over guiderails to raise or lower the skimmer.
 2. The skimmer as claimed in claim1 wherein the conveyor is an articulated open mesh defining cavities forcollecting and transporting the heavy oil or bitumen and wherein thepusher mechanism is a press roller adapted to press the heavy oil orbitumen from the cavities.
 3. The skimmer as claimed in claim 1 whereinthe frame comprises four bearing-adjustment mechanisms for adjusting therelative position of the left and right bearings of the drive sprocketand the left and right bearings of the drum.
 4. The skimmer as claimedin claim 1 further comprising a trough-tensioning mechanism having aplurality of spring assemblies connecting the frame to the trough forelastically holding the trough at a predetermined distance from thelower flight of the conveyor.
 5. The skimmer as claimed in claim 1further comprising a funnel and splash guard at least partiallysurrounding the drive sprocket for guiding heavy oil and bitumen intothe holding tank.
 6. The skimmer as claimed in claim 1 furthercomprising a lower shear plate disposed at the drum, wherein the lowershear plate has a knife-edge for cutting away bitumen or heavy oiladhering to the drum.
 7. A skimmer comprising: a frame for supporting adrive sprocket and for supporting a drum; a conveyor driven around thedrum by the drive sprocket, the conveyor defining a downwardly movingupper flight and an upwardly moving lower flight; a trough disposedbelow a portion of the lower flight; a pusher mechanism disposed at adischarge opening to force bitumen or heavy oil from the conveyor intothe discharge opening; a shear plate disposed at the drum, wherein theshear plate has a knife-edge for cutting away bitumen or heavy oiladhering to the drum; and an automatic depth control system forcontrolling a depth of the skimmer by controlling hydraulic cylinders tocause wheels of the skimmer to roll over guide rails to raise or lowerthe skimmer.
 8. The skimmer as claimed in claim 7 wherein the conveyoris an articulated open mesh defining cavities for collecting andtransporting the heavy oil or bitumen and wherein the pusher mechanismis a press roller adapted to press the heavy oil or bitumen from thecavities.
 9. The skimmer as claimed in claim 7 wherein the framecomprises four bearing-adjustment mechanisms for adjusting the relativeposition of the left and right bearings of the drive sprocket and theleft and right bearings of the drum.
 10. The skimmer as claimed in claim7 further comprising a trough-tensioning mechanism having a plurality ofspring assemblies connecting the frame to the trough for elasticallyholding the trough at a predetermined distance from the lower flight ofthe conveyor.
 11. The skimmer as claimed in claim 7 further comprising afunnel and splash guard at least partially surrounding the drivesprocket for guiding heavy oil and bitumen into the holding tank. 12.The skimmer as claimed in claim 7 further comprising an upper shearplate disposed at the discharge opening, wherein the upper shear platehas a knife-edge for cutting away bitumen or heavy oil adhering to theconveyor.
 13. A skimmer comprising: a frame for supporting a drivesprocket and for supporting a drum; a conveyor driven around the drum bythe drive sprocket, the conveyor defining a downwardly moving upperflight and an upwardly moving lower flight; a trough disposed below aportion of the lower flight, the trough extending from the drum to adischarge opening; a pusher mechanism disposed at the discharge openingto force bitumen or heavy oil from the conveyor into the dischargeopening; and an automatic elevation control system for generating acontrol signal when sensing an elevation of the conveyor and forautomatically controlling the elevation of the skimmer based on thecontrol signal by controlling hydraulic cylinders to cause wheels of theskimmer to roll over guide rails to raise or lower the skimmer.
 14. Theskimmer as claimed in claim 13 wherein the conveyor is an articulatedopen mesh defining cavities for collecting and transporting the heavyoil or bitumen and wherein the pusher mechanism is a press rolleradapted to press the heavy oil or bitumen from the cavities.
 15. Theskimmer as claimed in claim 13 wherein the frame comprises fourbearing-adjustment mechanisms for adjusting the relative position of theleft and right bearings of the drive sprocket and the left and rightbearings of the drum.
 16. The skimmer as claimed in claim 13 furthercomprising a trough-tensioning mechanism having a plurality of springassemblies connecting the frame to the trough for elastically holdingthe trough at a predetermined distance from the lower flight of theconveyor.
 17. The skimmer as claimed in claim 13 further comprising afunnel and splash guard at least partially surrounding the drivesprocket for guiding heavy oil and bitumen into the holding tank. 18.The skimmer as claimed in claim 13 further comprising a lower shearplate disposed at the drum, wherein the lower shear plate has aknife-edge for cutting away bitumen or heavy oil adhering to the drum.19. The skimmer as claimed in claim 18 further comprising an upper shearplate disposed at the discharge opening, wherein the upper shear platehas a knife-edge for cutting away bitumen or heavy oil adhering to theconveyor.
 20. The skimmer as claimed in claim 13 further comprising anupper shear plate disposed at the discharge opening, wherein the uppershear plate has a knife-edge for cutting away bitumen or heavy oiladhering to the conveyor.
 21. A method of skimming heavy oil or bitumen,the method comprising: disposing a skimmer having a conveyor in a waterenvironment contaminated with heavy oil or bitumen; operating theconveyor of the skimmer to recover the heavy oil or bitumen from thewater environment; and automatically controlling a depth of the skimmerusing an automatic depth control system that receives a control signalfrom a depth sensor connected to the skimmer by controlling hydrauliccylinders to cause wheels of the skimmer to roll over guide rails toraise or lower the skimmer.
 22. The method as claimed in claim 21wherein operating the conveyor comprises: pushing heavy oil or bitumenfrom cavities of an articulated mesh forming the conveyor using a pressroller disposed above a discharge opening; and cutting away heavy oil orbitumen adhering to the conveyor using a knife-edged shear platedisposed at the discharge opening.
 23. The method as claimed in claim 22wherein operating the conveyor further comprises cutting away heavy oilor bitumen adhering to a drum around which the conveyor travels by usinga second knife-edged shear plate.